The Environmental Protection Agency should have conducted a more detailed scientific review before determining two years ago that greenhouse-gas emissions pose a threat to public health and welfare, according to a report issued Wednesday by the agency’s Office of Inspector General.

“This review did not meet all [Office of Management and Budget] requirements for peer review of a highly influential scientific assessment primarily because the review results and EPA’s response were not publicly reported, and because 1 of the 12 reviewers was an EPA employee,” the study said.

Although the IG probe — requested by the top Republican on the Senate Environment and Public Works Committee, James M. Inhofe (Okla.) — will do little to affect federal climate regulation, it provides fodder to those who question the government’s role in addressing global warming.

The investigation did not examine the scientific evidence underpinning the EPA finding of a connection between human activity and global warming over the past half-century.

However, Inhofe said, the IG’s conclusions raised the question of whether the administration should have concluded that carbon dioxide and other greenhouse gases qualify as pollutants under the Clean Air Act.

“This report confirms that the endangerment finding, the very foundation of President Obama’s job-destroying regulatory agenda, was rushed, biased, and flawed,” Inhofe said in a statement. “It calls the scientific integrity of EPA’s decision-making process into question and undermines the credibility of the endangerment finding.”

EPA spokeswoman Betsaida Alcantara defended the agency’s approach.

“While we will consider the specific recommendations, we disagree strongly with the Inspector General’s findings and followed all the appropriate guidance in preparing this finding,” Alcantara wrote in an e-mail. “EPA undertook a thorough and deliberate process in the development of this finding, including a careful review of the wide range of peer-reviewed science.”

The IG report concluded, however, that the agency met the legal requirements for issuing its “endangerment finding,” which provides the basis for federal limits on carbon dioxide from power plants and big emitters. It focused largely on a technical question of whether the supporting material for the rule amounts to a “highly influential scientific assessment” as defined by the OMB.

Both the EPA and the OMB, which establishes peer-review guidance for such rules, said the Technical Support Document did not meet the threshold for a “highly influential scientific assessment, because it did not cover new science.

It is unclear whether the report will affect a legal challenge to the endangerment finding that several industries affected by the regulation have mounted in federal court.

Two lawyers representing greenhouse-gas emitters in Wash­ington who are not litigants in the federal court case said that the IG’s findings could damage the EPA. Joe Stanko, who heads government relations for the law firm Hunton and Williams, noted that the EPA described the Technical Support Document “as the underlying basis for its endangerment finding, so failure to follow peer review procedures could come back to haunt EPA in the [greenhouse gas] litigation.”

But Vermont Law School environmental law professor Patrick A. Parenteau said in an interview that he did not think this would bolster the plaintiffs’ case, because “the IG has concluded EPA has followed all the rulemaking procedures, and its decision is supported by the underlying science.”

Beyond the court case, House oversight committee Chairman Darrell Issa (R-Calif.) indicated that he might hold hearings. “This report raises serious questions that our committee and staff will further review,” he said in a statement.

Juliet Eilperin is The Washington Post's White House bureau chief, covering domestic and foreign policy as well as the culture of 1600 Pennsylvania Avenue. She is the author of two books—one on sharks, and another on Congress, not to be confused with each other—and has worked for the Post since 1998.

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